1. Cryogenic System Commissioning Summary Report
2019年1月17日
Cryogenic System Commissioning Summary Report
He Kun , He Chongchao, Ding Meiying, Zhang Yu,
Wang Yaqiong, Li Na, and Ye Bin
June 5, 2018

2. Content
Introduction
Commissioning procedures of cryogenic system
Acceptance testing of helium refrigerator
Commissioning of hydrogen cycle
Summary and questions

3. Introduction
Purpose of cryogenic:
Providing supercritical cryogenic hydrogen to neutron moderators, working at 14~15 bara, K. Hydrogen critical temperature is K, and critical pressure is bara.
Main equipment:
Helium refrigerator with capacity of
Hydrogen cycle, include hydrogen loop cold-box(two cryogenic hydrogen pump, hydrogen-helium heat exchanger, ortho-para convertor, heater and so on)
Accumulator cold-box;
Cryogenic pipes.

4. Cryogenic system flow diagram
Introduction
Cryogenic system flow diagram

5. Introduction Compressor and oil separator Storage tank Helium cold-box
Hydrogen cycle cold-box and accumulator cold-box

6. Commissioning procedures of cryogenic system
2019年1月17日
Commissioning procedures of cryogenic system
1. Acceptance testing on the helium refrigerator was completed in August, 2016, after the installation of the helium refrigerator.
2. After installation of hydrogen loop equipment and simulated load, hydrogen loop uses helium instead of hydrogen and cooled down to 20 K from January to April, Then, hydrogen loop using hydrogen as working medium, cooled to 20 K, from April to May.
3. After removing the simulated load, cryogenic system and moderators are jointed commissioning on June, 2017.
In order to ensure personal and device safety, excellent safety interlock is the precondition.

7. Acceptance testing of helium refrigerator
Compressor, oil separator and helium cold-box are installed on July, In order to ensure proportion of the impurity under 5 PPM and total under 10 PPM, activated carbon need thermal desorption and liquid nitrogen purifier need to purify. Using the refrigerator internal heater as thermal load. The outlet of turbo temperature set 16 K, running 24 hours stable, and the capacity is
Refrigerating capacity /W
Discharge pressure
/bara
Suction pressure
Post-expansion
temperature /K
temperature / bara
Flow
/g/s
700
8.64
1.541
14.5
1.76
83.8
1400
10.11
1.798
14.9
2.01 96
2300
11.86
1.97
15.8
2.25
104

8. Acceptance testing of helium refrigerator
Helium refrigerator running state at 2300 W

9. Commissioning of hydrogen cycle
In early January 2017, cryogenic system installation have been finished. Simulated load was used instead of neutron moderator, simulating the heat load of neutron moderator. Heat load of two neutron moderators corresponding to 200kW proton beams which is CSNS design objective is 320W and 240W, respectively. In order to ensure safe, commissioning work is divided into two steps. First, hydrogen loop uses helium instead of hydrogen, cooling down to 20K, and get preliminary control logic. Second, uses hydrogen as working medium, optimized the control logic.

10. Commissioning of hydrogen cycle
From January to April, we have completed the five rounds cool down commissioning of helium, and three rounds commissioning of hydrogen on April and May.
Cryogenic system running pressure is bar, and rupture disk pressure is 17 bara. The differential pressure of accumulator must below 1.5 bar. Therefore, pressure control is the key of commissioning. 。

11. Commissioning of hydrogen cycle
First round of helium commissioning
When Hydrogen cycle pressure increase, control logic have no venting logic at that time. Therefore, pressure fluctuate rapid cause chain protection.
Second round of helium commissioning
Modifying control logic, including venting and so on. In addition, needle valves were installed to reduce inlet gas flow. However, the differential pressure too high cause chain protection.

12. Commissioning of hydrogen cycle
Third round of helium commissioning
Modifying control logic, reducing differential pressure is the key work. Though differential pressure was also rapid, we control the differential pressure in reasonable range by valve and we get success.
Fourth round of helium commissioning
Further optimize the logic and cooling down smoothly.
Fifth round of helium commissioning
Further optimize the logic so that cooling down to 20 K by one key.

13. Commissioning of hydrogen cycle
summary： We mastery how to control pressure by five round commissioning. We do leakage detecting by helium mass spectrographic method after commissioning. It prove that cryogenic system manufacture and install excellent.

14. Commissioning of hydrogen cycle
pressure
Frequency of pump
Temperature of exchange outlet
Temperature of exchange inlet
Flow
Cooling curve of helium commissioning

15. Commissioning of hydrogen cycle
Control interface of helium commissioning

16. Commissioning of hydrogen cycle
The volume of hydrogen cycle is 140L. physical property of hydrogen and helium have great difference. Helium density changes evenly from 300 K to 20 K. Hydrogen density changes rapidly, from 35 K to 32 K. It makes cooling down difficult.
Density
(kg/m3)
300 K
35 K
32 K
20 K
helium
2.4
35.7
hydrogen
1.2
20.6
51.9
72.9

17. Commissioning of hydrogen cycle
First round of hydrogen commissioning
In the beginning, cooling down was smooth from 300 K to 35 K. When exchanger outlet temperature is below 35 K, pressure changes rapidly, and it makes venting frequently. At last, cooling down is fail.
Second round of hydrogen commissioning
We try to make all the temperature point of hydrogen cycle are 35 K-40 K. Therefore, we set helium refrigerator 60 K. The refrigerator can’t maintain 60K, and temperature drop to below 35 K. This round commissioning is fail too, but we found that all the temperature point at 35 K-40 K will get high flow.

18. Commissioning of hydrogen cycle
Third round of hydrogen commissioning
In order to maintain refrigerator temperature 35 K, we close cold-box refrigeration mode when temperature is 35 K, and it makes all the temperature point of hydrogen cycle is 35 K-40 K successful. In this case, all the temperature point of hydrogen cycle drop to 20 k slowly, and cooling down success.

19. Commissioning of hydrogen cycle
Frequency of pump
Temperature of exchange outlet
pressure
Temperature of exchange inlet
flow
Cooling curve of hydrogen commissioning

20. Commissioning of hydrogen cycle
Control interface of hydrogen commissioning

21. Commissioning of hydrogen cycle
After hydrogen commissioning success, we remove the simulated load, and connect the neutron moderators. Cooling down method is same to third round commissioning. Cryogenic system run four weeks from August to September stably.

22. Commissioning of hydrogen cycle
Frequency of pump
pressure
flow
Temperature of exchange inlet
Temperature of exchange outlet
Cooling curve of hydrogen commissioning on August

23. Commissioning of hydrogen cycle
Control interface of hydrogen commissioning

24. Commissioning of hydrogen cycle
Cryogenic system run stably last December to now, proportion of the impurity maintain low。
proportion of the impurity on 15th, May

25. 2019年1月17日
Summary and questions
Summary ： Cryogenic system commissioning work plans early, and commissioning procedures is reasonable. Though commissioning time is urgent, we get the cooling method by several round commissioning. We attach importance to the safety of the hydrogen, and chain protection works well. During the commissioning, there is no safety accident. During the commissioning, all the equipments works well, and it prove that equipments are reliable.

26. 2019年1月17日
Summary and questions
Questions ： Refrigerator must be upgraded to ensure that refrigerator can maintain 35 K for long time. We have communicated with Linde to solve this problem. The flow resistance of ortho-para convertor is too high because of too much catalyzer, and the pressure drop is more than 1bar. On the premise of enough catalyzer, We need to optimize structure and decrease catalyzer to reduce flow resistance.

27. Thank you！